1. Field of the Invention
This invention relates to battery systems and specifically to a battery connection failure detection system.
2. Description of the Problem
Battery packs are generally made from a number of individual cells that are connected in series to provide higher voltages and/or parallel to provide higher current. A number of inventions address the fundamental issue of how to connect such cells including bolting, soldering, friction and welding methods.
A disadvantage of the existing connection methods is that they may all, at some point, be prone to failure. This can be caused by corrosion, physical impact, vibration or components coming loose. If bolts securing the cells become lose resistance increases and so does connection temperature. This could cause a fire. This is particularly troublesome in hybrid vehicles using high capacity and high voltage electrical storage systems for electrical motors.
Battery safety systems employ thermal sensors placed near the battery cells which are used to detect thermal runaway events where cells have experienced a catastrophic failure. This failure can occur during charging or discharging. It is hoped that electrically disconnecting the battery would halt further heating and prevent fire from occurring. Such sensors often operate based on a single temperature threshold, for example 80 degrees centigrade, as a point where battery operation is considered unsafe.
Battery safety systems occasionally include thermal sensors located on the electronic components that are used to carry the battery power. These components are often rated to withstand up to 175 degrees centigrade. Therefore, the temperature threshold used to determine mis-operation of such devices is usually set in excess of 100 degrees centigrade.
There remains a need for a battery safety system that can determine the health of the battery connections and can therefore take preventative action when such connections are found to be unhealthy. There further exists a need for such detection methods to be predictive of such failure before it reaches catastrophic levels.